Hydraulic fluid



.w u H G* O. .fr a r K ww S x 0.. N Y wwf.. m swmF R o E a T w l wwwa" m 7 5 4 L nw E7 om on 0 l on 3. m E wm M w om m 2 7J F. oo /o ...n o o.0v nu N i um oe m 0. w. 2 6 m m` n Oe .w m W mm F 6. a J O y o 0 y 0 6. 6m c 7 ,L L. os A n W /o C ..0 M m \\\6\ mT IL S vALE AB o \\W\ W. A 4.. .9., M 0.6 0/0 M O s 6 Z 4 0 0 O 0 O 0 w. M .w w w 5 a o. o o. o o. o. o o. 5. 5 I 05 O O 5 3 2 I .o 2 2 .l 32228 s 5252 509+ E 22228 s mSmS Nov. 4, 1952 Patented Nov. 4, 1952 UNITED .S TATE S E '2,616,854

HYDRAULIC IFLUID "Merrell Robert Fenske, State College, Pa., as-u 'S'ig'nor Yto the United yStates ofAm'erica as represented by the Secretaryfo'f the Navy ApplicationNovember 13,1943, Serial No.1510f17`1 v 1 claim. .1,

This invention relates .to .luids'for' transmitting `or absorbing energy vand,'.m'ore particularly, to a .new and improved hydrocarbon-base `hydraulic iiud suitable ier use in 'hydraulicallyoperated equipment, and to a novel method'by which theuid may fbe produced expeditiously.

Hydraulically operated mechanisms may roughly be classied. into vtwo typesyi. e., (1) ithose..wherein a Uhydraulic .Huid-.is employed :for

the purposeof transferring the actuating :energy tof various types of .actuating devices; and (2) those wherein aifluid isemployed .in a device designed 'to fabs-orb ordamp'en lshock. The .rst class o'f devices zi's exemplified :by :actuating 'equipment .for "landing-gears, Wing lflaps, l.'b'rak'es, variable pitch propellers, control and automatic vpilot steering' equipment, transmissions, fluid clutches, lire control devices, gun turret rotating mechanisms, steering' devices, eleva-tors,

'-hoiStS, 'and the like. Thesecond vclass o'f devices includes artillery recoil mechanisms, 'shock absorbers, arrestingge'arsyand the like'. y

In the eld of military, applications of"hy or'lower to "200 F; .or higher.

. ious sealingir'nedia likely 'to"`be encountered in 'dra'ulically 'operated devices, the reliability and 'the' precise functioning" of the 'equipment over extreme conditions-of use are o'f prime importance.H Wide temperature variations are cornmonly` enc-ounte're'dand therefore uniformity of hydraulic characteristics over a Wide "temperat'ie range is of utmost importance inthe 'selection of hydraulic `iluidsor military applications.

Among. the various .desirable characteristics for a vhydraulic .fluid .suitab1e..for the extremely ,severeconditionsof vmilitary useare good lubricating. qualitiesv over a .iwiderange of tem- .perature-zcondtions.4 For. this reason the-fluid shouldhave fa reasonably high viscosity at elevatedtemperatures andra .reasonablylow viscosityfat very low temperatures. rIhi.s.reo11.1ires.,.for exampler a fluid .having .a yiscositylof .faboutlo ,to` v10.0;-centistOlr-es.at 100. anda very-.low viscosity-temperature coeicient. vLubricating .qualities Yare especially r.important-in the case .of khydraulic pumps ,.uid `motors `andother .devices wherein. various v.sealing media lor..parts undergo `sliding:orrotaryfaction in valves, pistons and.. other. .mechanical parts. These. seals may compri-se various packings, leatheranda variety. of .rub-loerV compositions. The .fluid ymust provide lubrication. as .these sealing mediaJ .slide over various metal parts, otherwise, the 4*seals will vloetorn or abradedland .then.f.leak. `Good lubrication.. of .hydraulic pumps is of particular. importance .inasmuch as -suchpumps may generate `pressures, of A1,000'ormore pounds per `square inchand ,must operate atlhighvolumetric eili- .ciency.

it' is also desirable that the fluidrexnain c1631' hydraulic equipment; Itlis also desirable that the .uid possess 'good antiwear an`d"antirust properties and ybe'suiii'ciently nonvolatile to obviate Jthe -developmento'f atackycondition during repair of the equipment.

An 4object of tlfiepresentinvention lis to provide'a hydraulic'uid characterized bythe foregoing desirable properties.

Another' object Aof 'the invention is to 'provide a fluid which will permit the operation of hydraulically operated .equipment over an extremelybr'oad range of 'temperature conditions.

A further object is the provisionof'a lhydrocarbon-base' hydraulic "fluid that has a `low 'vis- 'cosi'ty 'at low .temperatures and which also possesses aireasonably'high Vviscosity and a low'volatility at elevated temperatures, Aso as to afford ample lubrication and sealingzagainst excessive high Vtemperature leakage;

A still 'furtherlobje'ct of the invention `is to provvide a uid 'of the character described, which has a high resistance to shear, that is, one wherein the viscosity breakdown bvsh'earis low when subjected to lservice conditions' where there is excessive throttlingg orwh'ere there is -the conversion of relatively large amounts of hydraulic energy into fluid friction and heat.

vStill another object of the .invention is to provide a 4me'thodoi producinga hydraulic uid of the character described.

An additional object of .theinvention is to provide a hydraulic. uidcharacte'rizedf by .little .change in properties `on..prolor1ged. low .temperature storage; .a verylow swelling actionon various rubber. sealing. media; av high. .stability against oxidation, .corrosion and viscosity change; .a relatively highash vand re point.; a very low rate .of change v.of viscosity with temperature; and `a relatively 'high fluidity.. at`.low temperatures, with ar low freezingpointand freedom from gelation .at very'low temperatures.

These and other objects of 'the .invention will be understood as` the .invention is .hereinafter more particulary described.

IV have found Ithattlie foregongob'jects may be attained by a combination of two ermore carefully, selected. components. Basically, the .combination 4hyrl'lranllic fluid 'fthe present invention comprises:

'(1) a substantially. Wax-free hydrocarbon- 'base stock having a 'boiling' point range Alying The base stock preferably consists substantially of saturated isoparafnic or naphthenic hydrocarbons: i. e., the base stock is substantially free of wax-forming components, unsaturates, aromatic hydrocarbons, and oxygenated and nitrogeneous hydrocarbon derivatives.

As regards the polymeric additive, the polymer (a) should have a molecular weight between about 5,000 and about 20,000; (b) should be sufliciently soluble in the base stock to produce a clear, fluid solution which is stable on prolonged storage at all temperatures within the range of at least 40 F. to +200 F.; and (c) should be used in an amount su'icient to produce an A. S. T. M. viscosity-temperature slope less than 0.60 and a viscosity of 10-100 centistokes at 100 F. Practically speaking, these amounts normally lie within the range of about to about 20%, on a weight per cent basis, the particular concentration depending partly upon the nature of the base stock, partly upon the nature of the particular polymer selected, and, partly upon the specific properties desired in the finished fluid.

VThe hydraulic fluid of the present invention, as briefly described above has particularly outstanding characteristics which will be apparent from an inspection of the accompanying drawing, in which Fig. l is a graphical representation of an A. S. T. M. (D341-39) viscosity-temperature plot for three fluids; and

Fig. 2 is a blending chart graphically showing the effect of various amounts of polymers on the viscosity and A. S. T. M. viscosity-temperature slope of several base stocks when blended in accordance with the present invention.

Referring to Fig. 1, the line I typies a conventional type of mineral oil having 20 centistokes viscosity at +100" F. Line 2 characterizes a desirable type of hydrocarbon-base hydraulic oil. Line 3 represents the viscosity-temperature relationships for fluids of the present invention. These three oils or uids, purely for purposes of illustration, have been matched in viscosity at +100 F. They can be so matched at any other arbitrarily selected temperature and it will be understood that the present invention does not relate exclusively to oils of 20 centistokes viscosity at +100 F., since the viscosity of the present iiuids may vary from about to about 100 centistokes at +100 F. By inspection of Fig. 1 it will be apparent that at 40 F. the centistoke viscosities of oils l, 2 and 3 are respectively: greater than 40,000, about 7,000, and 300. Thus the fluid 3 of the present invention has a viscosity' at 40 F. which is less than 1/20 the viscosity of the uid 2, and less than tion the viscosity of the base stock l.

In addition to a hydraulic fluids viscosity, its change in viscosity with temperature is of importance. It is possible to give this property a more or less quantitative or mathematical value by determining the slope of the lines on Fig-f 1, the value thus obtained (hereinafter called the A. S. T. M. slope) being very useful in blending. The A. S. T. M. slope for any of the lines drawn on Fig. 1 is of course the linear distance AB, divided by the linear distance BC. Thus it is found that the slope of oil I is 0.85; of oil 2, 0,73;

and of oil 3, 0.44. Specifying the oils viscosity and A. S. T. M. slope, therefore, defines the viscosity-temperature behavior of thatv oil over a relatively wide temperature interval. .With the foregoing explanation in mind, it will be apparent that by the use of a special hydrocarbon-base stock to which is added 5 to 20 weight per cent or more of oil soluble polymers of controlled niolecular weight, the viscosity of the base stock is increased from about 3 to about 15 times, and its A. S. T. M. slope is decreased 25 to 50 or more per cent.

Having now briefly characterized the hydraulic uid of the present invention, it will be convenient to consider in somewhat greater detail the nature of the various components. As a matter of convenience, the polymeric additives will first be discussed; thereafter the base stock will be considered; and lastly the method of incorporation will be described.

I. THE POLYMERIC ADDITIVES Referring now to the polymeric additive, a large number of materials of this type are available for use in accordance with the present invention. These materials include polymerized vinyl-type compounds such as the oxygen-containing vinyl polymers or the hydrocarbon-type vinyl polymers: for example, the polymers of vinyl ethers, vinyl esters, acrylic acid esters, methacrylic acid esters; or the polyisobutylene and polystyrene type of polymers. Polyisobutylenes and polymeric esters of methacrylic acid, particularly the higher esters such as the octyl esters and the like, are especially suited for the purpose of the present invention, these compounds being readily available under the trade names of Polybutenes and Acryloida respectively.

As previously indicated, the molecular weight of the polymeric additive is of great importance for several reasons. In the first place, in order to provide hydraulic fluids that can assimilate or dissipate relatively large amounts of hydraulic energy, either as useful work or as friction, without undergoing serious intramolecular changes resulting in a considerable viscosity decrease in the fluid, it has been found in accordance with the present invention that the molecular weight of the polymeric additive must be carefully controlled so as to lie within the range from about 5,000 to about 20,000 and preferably within the range from about 5,000 to about 15,000. Polymers having molecular weights within these limits do not show a serious viscosity loss under high shear or under conditions where there is excessive throttling or wire-drawing. Indeed, one of the most important discoveries upon which the present invention is based is the fact that the closer the molecular weight of the polymer is to the lower limit (namely, about 5,000) the more resistant the fluid is to changes in viscosity by shear. It is therefore possible to select a molecular weight within the aforesaid range to meet practically any shear requirements that may be imposed.

The molecular weight of the polymeric additive is also important because of its relation to the solubility of the material in the base stock at temperatures which range from 50 F. or below to above 200 F. In other words, it has been found that the solubility of the additive is of utmost importance, and molecular weight is, of course, one of the several factors in such solubility. indeed, olubilty is of such importance that tests 5 are:madeto'fascertaiirwhethenthefseiectedadditive ais satisfactoryfronizthis pointrofyieui. Adequate solubility is falsojudgedbyvisual: inspection of `their.' additive-for :any f insoluble materials; or

gel structuresi..` HoWever,;-. a much .more sensitive method; ot'. judginggsolubility is. .based upon.:v viscosity measureme'nts.f-y If. viscositiesaremeasufed, targubyf Sz-T. Mrlprocedure WM5-42T); .at subas-.Wel-h a's'xfat above-"normal temperatures; vand thesev measurements,-repeatedat successivefftime intervals offhoursf or-.days, anyyincompatibility or insolubilityl forA polymemand. .base stoclrfbecomes readilyidiscernible.by.;varying..and'non-reproducible -viscosity measurements. It is` also :sometimes desirablezasa 'test-of .adequate polymer.",solubility to measure `the.-viscosity at different ratesv of shear overthe-rangeironrabout: 200110l 2,000 reciprocal seconds. evaryingsorv erratic* viscositygat these" variable shear ratesiisfalso evidence 'ot inadequate solubility;

In most ofthe applications intended-orsthe present... improved?. hydrocarbonebase: hydraulic uids; `good viscosity-stability under conditions of high. shear isz-essentials. the viscositywof aspecic-iiuidfor aifspecific. purpose is` carefully' adjusted to. meet cer-tain,- operating requirements over ai` wide .temperature range.. it.l .istoi course vitally; important. i that: the 1viscosity does".v not change undulyqwith, use. Y A decrease. inf..viscosity Will-.be primarily objectionable at' normal or elevated .temperatures because..=there.` Will be:` :more leakage, more: slippage in mechanical parts,l more diiiicultyin attaining fthe required pump pressures and displacements: and-.mores wear.'A in certain parts of' the-hydraulic system. An. increase-"fin viscosity during-lisais objectionable 'atlowtemperatures,. for certain parts'of the hydraulicv equipment may be sluggish;` not capable of. being.' coordinatedwithiother operations,l or mayl evenfbel come.- inoperative because ot the. excessive Viscosityr` at low temperatures;

Under conditions of high shear or Where there is excessive throttling or Wire-drawingl ofA the iiuid, (as Where aiiuidflows withhigh'pressure drop through. short distances in.` turbulent' flow) some of the polymers ytend. to depolymerize'.` In

View of the. rfact that.` in the .present fluidsg.:` the sureis: then unloadedfthrougha suitabl pressure relief:`.yalve,.. whereupon the:fluid;v is'zfag' theapumpi o,.repeat'thesoperatiorrtor.cyj arbitrarily .selectedt Vnumber.. 'of .cyclesfis`J depending uponfthefseverity 'ofcpolymeifpbralsdovvndesired-z.` The `flower.':theatemperatur .at which this opertiomiscarried;C out,:.thefmore.

'stafedito r square--inch f as piston4 .merio substances-hasbeen their viscosity-in- 6 settare-itesm..Arriseositmdecreasefby'this shearing operation, odiperszcenti or. less; is .'prefe'rreds..

It 'zwill .befunderstood.:.thatevariouspolymeric substancesr can .be used iny combination. tov produce thefpreser'it improved; types ofhydrocarbonfbase hydraulic .tluidsa For'zexample, several diiiere'nt molecular-:weight ranges 'of y.the same polymer weights... can also be used. together, althoug'h in this' case:itis-preferabletolim-it .the amount: Aoi' each polymer inrtheinalviiuidto' aboutrIO to.15 lcent ofi: the *..totall uid.. Thus, for.. example, polybutene and. acryloidmay be;y presenttogether ini-.the sax-ne: fluid-ibut4 it isipreferableto limit the percentagel- Aof ."each.,. when` :.usedf in: .about equal proportionsytozaconcentration. of. about 1.0 to .'15 per'centi.l If.. onepolymer vis used in' much.V greater proportiomthan-the roth er,1 then the predominating 'polymer may gbepresent. in amounts' in. excess offl :percent-, while-thef-.Dolymer in. minor .proportion may be limite'dtoVl to 10` per centconcentration..in..the.iinishecb fluid;` There aref'certain 'advantages in them-blending of polymers,

,fforlit s.thereby. possible. .to takergreater advantageoi` specific properties fpossessed by any particularipolym'en.v Forexamplea polymer having good, viscosityeincreasing properties4 can thereby beifiutilized aiongwith .onehaving particularly .goodfslopeedecreasingproperties to givea greater range-oiciziscosity and-A. S.;-T.M..-slopes than that convenientlysor economically .obtainable by :either polymer:alone,` v

Gneeof. the difculties: with... hydraulic` iiuids composed ot .highlyrened.mineraloil andpoly- Stability in servicef- In. somecasesV or prolonged use`f,.theviscosity would decrease, while in other cases-.f `its/'Would c increase y300 -to .800' per centV or ...more-s` 'llheresu have Y. alsa-been. instances of` the polymer precipitating. from the solution. None oiLtheSebh-anges can be. tolerated infcertain hydraul-icapparatus,v .where delicate parte, such as pilot,balanced` andf-relayfvalves havetofbe actumanner.:

In-f-accordanccwith a.further aspect of. the presentinvention; it hasbeen found` that exceptionalayiscosity-stability can .be imparted to' hyvdrocarbonetype hydraulic fluids .containing .high

molecular Weight polymer-ic substances yby incorporatingatherein a small amount of substances ofthe-.-c1`ass-of materials known as 'oxidation inhibitors such as.those usedin transformer, turbine. and-.1. other: low'v viscosity lubricating oils.

Such materialsin:proportionsffrorn about 0.2 to about 2 weight per centhaye been found to have verybeneficia l.efleets,- both1 on .the 'basestock and'o'rithepolymeric. materials-'.-

nother.difiicultyI heretofore experienced With certain-.hydraulicuids arisesfrom the formation ogunimy. andins'oluble materials upon extended usage,` .andl:;the... etching andpitting. of-...delica'te metal parts;x Thistroublesome and.` undesirable disadvantage mayfbeobviated in accordancefwith the present`- invention-.by .the -use. of. the aforesaid oxidation inhibitors. II. THE BASECSTOCK" fisprevrous'i'x'r.pointedout;Y the base stock" or fluid" Ai1i`whic`i`1 th'e'poly'm'er, is' dissolved', contribut i manyimpcrtant :ivays 'to' the :properties of th -ishd 4'h'ycfrtitille V`fluid." The base .Stock l'aywc'o'i'mis'"Specific, more "0lf1eSS individual 'evaporate excessively.

such as synthetic rubbers.

that this can be avoided by excluding aromatic sam-6,854

m'ay be produced from' petroleum'and1 therefore contain a varietyof hydrocarbons; Regardless of its chemical composition, however, the `base *stock must be low freezing; i; e., free from solid 'sep'aration at temperatures of 40 or lower.

It .must be relatively nonvolatile, so as' not to For the most part, vit should distill in an A. S. T. M 'type of distillation within the range from about 400-F. to about 700 F. at atmospheric pressure. It must not contain any unstable or corrosive materials. Itis 4important that the hydraulic fluid should neither swell nor shrink excessively the sealing media, It has been found andv other highly unsaturated hydrocarbon types, and by having a substantial 'proportion'of iso- "parailinic hydrocarbons in the base stock. It'has also-been found that rubber swelling and shrinkage can be controlled completely by selectingand specifying certain properties of the base stock to 'be subsequently described.

Where it is desirable to prevent excessive evaporation and the formation of tacky or sticky films lvvhen'layers 'of the hydraulic fluid are-exposed" to the atmosphere, it may' benecessary to 'use blends oftwo or more base stocks of dierent 'boiling ranges. Thus, 'for example, one portion 'or fraction may have a substantial part boiling in the range of about 400 to 500 F., while the other portion or fraction mayY have a substantial part boiling in the range of 650 to 800 F. When polymeric or other high molecular 'weight substances are added tobase stocks comprising the aforesaid blended base stock, the viscosity-tem- `vperature coefcients or A. S. T. M. slopes are especially good in that the viscosity of theflnishe'd -uid changes relatively little' with temperature,

pound has 3.3 and 51.3 centistokes viscosity at.

+100 F. and 40 F., respectively; an AIS. T. M. slope of 0.737; and a 200 F. anillne point. Tetraisobutane is obtained by dimerizing diisobutylene and hydrogenating the resulting material. Y Itis -also obtainable by polymerizing isobutylne toV the tetramer stage and then hydrogenating. 4

Likewise, alkylates boiling i'n the range of 400 to 700 F. with low freezing pointsand substantially olefin-free are also usefulas base stocks. They are characterized particularly by their high aniline points, being above 190 to 200 1i. These 'valkylatesar'e soparafnic inA character and are produced by alkylating and polymerizing oleiins with paraiiins, st'arting'with the lower` molecular weight olefin and paraffin hydrocarbons having usually 3 to 6 carbon'atoms per molecule. The alkylates are attractivefor the -reason that rubber swelling, or shrinking, or general deterioration,

'is usually'low with this type of hydrocarbon," Y The falkylates may be used either as the principal component of a base stock or for mixingwwith other hydrocarbon stocks to improve' their behavior toward rubber.. Hydrocarbon polymers inthe molecular. weight saturated in character, are also suitable as base fstocks. Such materials may be obtained Yas by- 'products from polymer gasoline manufacture "They may be derived from thegasoline lby dis-515 -ever, the., acid treating process hasthe disad- Y 70 `range 'of about 150 to` r300 that areiess'entially ti1lation, then hydrogenationtto producexisaturated hydrocarbons, and, if'necessary, dewaxing to attain the desired low freezing point.

In addition to the foregoingi'soparanic materials from polymerizationand alkylation processes, it is possible to produce base stocks by alkylating aromatic hydrocarbons Awith oleiins and subsequently reducing the aromatic part to "a naphthene structure, thereby producing synthetic naphthenic-paraffinic materials.

Perhaps the most convenient and extensive source of base stocks is to be found in petroleum, and more particularly in petroleum fractions boil- "ing within the range of about 400 F. to about 700 F. at atmospheric pressure. To prepare-such fractions from petroleum, it is desirable to carry out the following steps, approximately in' the orderlisted: (a) preliminary chemical treatment; "(b) distillation;"(c) dewaxing, when necessary; (d) dearomatization; and (e) clay filtering and blotter pressing.

(a') Preliminary chemical treatment-It is de- 'sirable to remove naphthenic' acids, phenolic compounds, nitrogen'bases and sulfur compounds `from-that portion of petroleum being processed f into base stock. A caustic and acid wash removes most of these materials', the methods and'e'quipment for performing these operations being well vknown and available in many reneries.

(b) DistiZZation. -Suitable equipment for the relatively close fractionation-of the 400 to 700 F. portion of petroleum is available at many reiineries.' Varying the boiling range of the base stockl usually varies its viscosity, and this in turn may vary the viscosity of the iinished hydraulic fluid. As already pointed out, it is freouently desirable to thave two portions or fractions available for making the base stock. These portions are produced b'y suitable operations and control of the distillation equipment. vIn certain cases it may be desirable that the boiling range of each portion be not more than 50 F.4 to 75 F.

(c) Dewaing.-In those cases where Wax separates from the petroleum fraction at low temperatures, it is necessary to eiect its removal =along more or less conventional lines, with the exception that the dewaxing temperatures may have to be reduced to 40 F. to 70 F., and upwards`of 50 per cent may separate as- Wax. In '-general, the Wax separates easily, and the resulting wax-free oil is very valuable for further processing into nished base stock. Filter presses -or rotary continuous Vilters may be used. Solfvent dewaxing may or may not be required. In those instances where wax separates,` it is cus- 'tomary to refer to these petroleum materials as being parainic.` In those cases where there is no -Wax,'the petroleummaterials are commonly des- .i'gnated as naphthenic.

(d) Dearomatz'zation.-To keep rubber swelling at a minimum, it is esss'ential to remove aromatic hydrocarbonsfromthe base stock. In general, .two 'methods of dearomatization are available.

:The first methodu-tilizes sulfuric acid treatment -65 in arnanner similar to that commonly used in Ymaking white oils or'medicinaloils. The other .procedure involves the use ofla selective solvent #to dissolve out the aromatics.. i .Y

5v Ihe -acid treating Vmethod has thefadvantage of favoring the "removal of;:any more', reactive components which might be present in the starting material, and which are undesirable in the .finished stock, suchas, -for' example, certain -sulfu-r, nitrogen and oxygenated materials. How- 9^. vantage that certain? compounds-.are formed and assimilated by u the .oil .iunlessf. subsequently removed. Such .compounds includesulfonatesand Nevertheless, .the particular method of dearoma-1 tization selectedis .largelywa matter of reiinery practice and convenience.

(e) Clay filtering and. blotter pessirtgrffell stocks that have been dearomatized bysulfuric acid treatment should; -preerably be., given. a light clay treatment or. some equivalent treatment .in order to eliminate. small :amounts vof sulfur or oxygenated materialsv that. may. .remain in.A the oil even after 'the causticxor1 waterfwatsh. l ySuch materials appear. to bercadilyzadsorbable by Vthe clay. Following thisfclg/ treatment, ,zand `asa final precaution,4 the-.fluid is.f preferably passed through a inter. rpress.c011.11.airline :heavy paper Q1 otheriequivalent lter ,Inedillmin Oldl '1.39 dimi" natefgany `clay f orpther foreignpartieleswhich may 'be present :the Oil, @HdfSSSQf'iQ remOVe traces of moisture. This `fina-l step insures a perfectly clean;:stoiclif.and.` .particularly Idesirable for.. hydraulic luiidS a'fzheticomein contact .with complicated and delicate mechanisms.

Ingeneral, ,rarafnc :Stocks are preferred to' naphthenic stoeksfbecause, :for a given viscosity, they .usually have less yeffect on; rubber, Jthey .are somewhat less -volatile,.and .they .usually .have va will be understood that 4the..,diigerent types of stocks may `be :blended-so that Vthemore desirable properties -of one stockgmay` `be .used to .enhance that of anotherstock. :Thebase stock preferablyr nrimoonronfrrou Incorporation of' the jadditives`"inthe'v base stocks in accordanceWiththe'present invention can be understood by reference .to'Fi g.` 2 which is a blending chart; showing :T .theI 'manner jin which various high molecular weightf'polymeric substances affect both theviseosity and the A.' S. T. M. slope, when added in various amounts to ldifferent. base stocks. VPoints D, E, F, and G represent different base stocks such as derived from y petroleum. Point D represents a low viscosity base stock, boilingover the range of about 430F. to 460 F. at atmospheric pressure. PointGfjrepresents amore viscous stoclg. boiling inthe'range of 650 F. to 800 These two stocks ,maybe mixed or blended to give other stocks having various proportions of stocks D and G. For example, point Elmayfrepresentaspecic stoclcwhich may be prepared. fromA petroleum;or'itmayrsalso represent a mixture otiaboutl weightzper cent stock Dgand40-weigh per cent stockiG. `.f 'Ilrearsam'ejis true for-stock 1F. It mayibe.a:separatelyLprepared material, or'.4 a .mixture .ofaboutu percent, stock D and 60 per cent sl',o,ck..,(lv.l

Curve 4 of Fig.2 `representsthe manner in` which the A. S. T. M.. slope and the 'viscosity change whenyarious .amounts of polymerized octyl methacrylate .of .about 10,000 molecular weight, an Acryloidjf .are added to Astock D. rIhe percentages on the curve (e. g., '6, rand 12 per centrepresent .the .weight per cent polymer present in .the fluidv at .these respective points.

Curve Ylishows these same relationships where the polymercomprises Polybutene 4of ab`out.12,000 molecular Weight (fPolybutene vB12) Vto base stock E. `Curve. 5. shows"'the results obtained when polymeric `octyl,.Qn'ieithacrylate of about 10,000 molecular weightan -Acryloi d,. isused instead of the Polyloutene in jbas'e.stock"E,"the percentage iigureson curvefi .beingr the'weight percent Acryloid type polymer present inthe fluid .at the points..,indi`cat-ed.l

Curvev 1 portrays .thefslopefjviscosity relationships or Ithe various indicated percentages of the .same fAcryloid-f-.when itis .blended into base stock F, while .curve .8 .alsoshows theser same relationships for .blending .with r'.Polyloutene B.-12 instead of the Acryl'oid. "Similar curves for other. base stocksandpolymers can be drawn inv an analogous manner. Y`liirthermore,' the jViS- cosity. scale can .beat .any `s e'lggeoted temperature, such as v .40". F., `o E.; +100 .+21or., etc. Similarly, the ,A. SNI. slopemay be expressed for.any arbitrarily .selectedtemperature interval. Each` polymer willhavea more or less characteristic curve. Some.wil1 increase. 'the ,viscosity with respect to a decrease Ain .slope more than others. In general, .the.blending curves for;anyv one polymer in different .bases'tock -will vroughlyparallel eachother.`

The viscositytsoale could .be .extendedfupwardly to Vany desired yalueand .the blending. curves would simply. be smoothfextensions in an upward direction of thoseshownfonFia?. Eorpurposes of this mvention, ,fluids `hauing viscosities at F. in theQregiono `10 to T100 icentistokes, and 4more .particularlyinthe range of about' 151to about 60.. centi stol esf,a't ;lI-.10.01E.`,' are'oi'principal concern. .lx'Ihis viscositymange is suitableffonhydraulic fluids ,f or. airplanes, `T`automotive vehicles, ships, .artilleryf .recoil ..mechanisufis, and Various shockaloscurbingY .devices "T o permit' adequate operation oyer a .wideltemper `t rerangeithat is, here .-.acb F....andiloweio to .1t-i200 F. `and higher, -it. is,.preferred. that 1 fluids ,of these viscosities 14have A. -S. ,M...slope`s lcelo vvl'j.0`.160,'y and preferably ,belde/.0.55. Fig. ,2 shows the .manner in wh-ich. this` is accomplished. ...It is clear ,that theV iinaltehydraulicfluid hasa .viscosity Severalfoldygreater :than .that ofjljthe 4.base stockv into which:theapolymergisqgblended, nd also `.that the slope; of-.thenal :fluidois onlyia traction .of `that o'fl. the lbaseixstock T .obtain .grshed .uds...of thelowest Mrlsloperit highly desirabl'e thatthefraslopezzof the: base. sto.ck,f..-itself, be as low as possible.

If the nished iiuidrc'QnaliS two or more polymers,t-,the-blendng.curage willlie proportionately between ...the blending ...curves V..iorthe separate polymers For ...examplaf if fPolybutene: B412 and the'..aboveementioned fiecryloid are added in `equal proportions .tdbasel sto'clrlili...` on K14-fig.. '2, tha-blending curyejfom this.v eoblend fof... polymers will aloe. roughly.-tmidwaybetween l.curves .5 .and Gaonjlif Ingtpreparingathetfnishedhydraulic iiuid, care is exercised in dissolving the polymer in the base stocks, for the rate of solution is apt to be low and it is necessary to avoid overheating and thermal decomposition. In general, blending temperatures are not permitted to exceed 350 F. and wherever possible the free access of air is not permitted at such high blending temperatures, for otherwise undesirable and unnecessary oxidationis apt to occur. It is usually desirable first to prepare carefully a concentrated solution of polymer in the selected base stock (e. g., a 50 weight per cent solution) and then blend the concentrated solution with further amounts of base stock as needed. It is easier to obtain a perfectly homogeneous solution by this method of incorporation.

' The oxidation inhibitors used to stabilize these hydraulic iluids should be soluble in the fluids in the amounts required, both at low and elevated temperatures.- Their presence must not accelerate the corrosion of the more common metals, such as steel, copper, bronze, aluminum and magnesium. They must not change with use from soluble to an insoluble form, and thereby form precipitates aptV to obstruct small-fluid passages. Suitable inhibitors comprise one or more of the following organic materials: alkyl or aryl phenol or hydroxy suldes; aromatic suldes, disuldes, mercaptans, or thioethers; aromatic amino suldes; sulfurized fatty acid esters, such as sulfurized sperm, lard, and rapeseed oils; alkyl or aryl esters of phosphorous acid; mono or diaryl amines; and phosphatides, such as lecithin. In certain cases similar proportions, namely, from about 0.2 to about 2 weight per cent, oi metal deactivators are used along with the oxidation inhibitors, in order to retard or nullify the 'powerful oxidationV accelerating eiects of vcertain metals, notably copper and its alloys,

and steel or iron. Many oxidation inhibitors themselves have this property of metal deactivation. Thus oxidation inhibitors having sulfur in the functional group are also effective as metal deactivators. Certain aryl amines are also effective, especially toward copper.

It will be understood that other materials may be added to the hydraulic'fluid to increase the lubricating value, reduce wear and seizure and prolong the life of fast-moving, heavily loaded, mechanical parts. Thus, from about 0.5 to about 2`weight per cent VVof tricresyl'phosphate or dilauryl phosphate are particularly eiective.

p In order still more clearly to disclose the nature of the present invention, two specific embodiments will now be described. One of these examples illustrates the production of improved hydraulic uids from a wax-free stock using an Acryloid polymer vwhile theiother example describes the preparation of-a typical fluid starting with a waxy stock Yusing polyisobutylene polymer as the additive. It should be clearly understood that these examples are given purely by way of example, and arey not to. be construed aS limiting the spiritor .scope of the appended claims. Y

Y Example I A commercial gas oil fraction from a renery pipe-still was obtained from crude typical of Colombian or Winkler production. This gas oil comprised approximately 30 per cent of the crude and showed no sign of wax separation at temperatures as low as -100 F. This pipe-still fraction was then refractionated in an efficient fractional distillation'tower toobtain a heart-cut comprising approximately 10l per cent of the original crude or about 30 to 35 per` cent of the pipe-still gas oil. This heart-cut had an atmospheric boiling range of 400 to 550 F.; an aniline point of about 150 F.; a viscosity of 2.3 centistokes at F.; an A. S. T. M. Viscositytemperature slope of 0.86; a pour point of less than 90 F., with no evidence of a cloud point above this temperature; and a flash point of 200 F. After an acid-extraction treatment described below, this heart-cut was used as the base oil.

Also recovered from the refractionation of the commercial pipe-still gas oil stream was a higher-boiling fraction to be subsequently used as the anti-tack component of the nished hydraulic iluid. This higher-boiling fraction comprised approximately 30 per cent or the pipe-still fraction, or approximately '9 per cent of the original crude. It had an atmospheric boiling range of about 600 to 800 F.; an aniline point of 180 F.; a viscosity of 10 centistokes at 100 F.; and A. S. T. M. viscosity-temperature slope of 0.86; a pour point of -60 F. with no evidence of clouding above this temperature; and a flash point of 300 F. The anti-tack component was used to reduce the volatilization of the base oil, and thereby avoid the'development of a sticky, tacky lm upon exposure of the nished oil to the atmosphere. y v

These two fractions described above were then acid treated, this being done either on the separated components or on a mixture thereof. Where the components were acid treated together the fractions were mixed in the ratio of 3 parts by weight of anti-tack to 7 parts of base oil. The acid treatment was carried out by vigorously agitating for a period of time an emulsied mixture of equal volumes of the oil and 96 per cent or stronger of sulfuric acid. The mixture was then allowed to stratify, the acid layer drawn oi, and the oil layer washed once with water, once with 5 per cent sodium carbonate, and twice more with water. The oil layer was then drawn off, free of water. This procedure removed the bulk of the aromatic-type hydrocarbons. The oil layer was then clay-treated by the addition of one pound of Super-Filtrol (or any other similar activated clay) for each 25 gallons of oil, with vigorous beating for Y15 minutes. Theclay treatment effectively rid the oil of any milky suspension carried over from the water and sodium carbonate washes after acid treatment; it also served to remove' those by-products of sulfuricacid treatment such as sulfates, sulfonates, etc. which cause intense discoloration upon any subsequent heating.

The following'illustrative properties result, depending on whether the two components of the base stock were acid-treated separately or together:

The base stock noted here represents the mixture of approximately 3 parts by weight of antitack oil to 7 parts by weightlof base oil.

The. recovery of oil from the acid treatment was approximately 70. per cent of the charge. In

termsof the original crude,`l` this amounted :to

about 17 per cent, or.-about''21 ipericentoff'lthe original pipe-'still gas oil. y 1t should valso be l.no-ted that the product obtainedfromthe acid. treatment in any case had a-neutralizationnumberof about 0.05v milligram of potassiumhydroxide'per gram of oil. In thecase thef neutralization Vnum.- ber exceeded 0.10, `the oil was.againlwashedlawith sodium carbonate and water.

' `Where theacid treatment had\beenicarriedfout on thai-base oil andvanti-tack.separately; then these tWo materials "-Werekblendedfatl this stage in the same ratio of 3 parts byfw'eight of-antitack to 7 parts by weight of base oil toproduce the"base stock. '-Wher'e the .acidtreatment had been -`carried out yon vtheuba'se:fb ndcantitack together, then the. acidtreated, clay-itered material constituted the :base stock.

`solution slof` active ...fileryloidN4 in fa petroleum-.bil

Viscosity 'at 130W?l 110.0 centistokes Viscosity at100"F --21'36 centi/Stokes Viscosity at '-`40F `i450 cent'stkes A. S. TIM. slope 130 to 40 F ."0.55 n. l Aniline point ,..Vm 179 F. Pour lpoint --75'F. Cloud pointfr 11.. ...f e75 F. Flash point 210 F. rire. point. 230 F- Neutra ization number .0.08 mgLgKQI-I Eample II A commercial fraction of a Pennsylvania gas oil having a very narrow boiling range, the 10 and 90 per cent atmospheric distillation points being 415 and 435 F., respectively, was used, this material being produced in a continuous fractional distillation unit operating at atmospheric pressure using Pennsylvania gas oil as the feed stock. The properties of this material were as follows: a fiash point of 200 F.; a

viscosity of 1.9 centistokes at 100 F.; a pour point of -20 F.; and an aniline point of 150 F. It comprises approximately 2 per cent of the Bradford Pennsylvania crude. After de- Waxing and acid treatment, this cut was used as the base oil.

Another commercially produced Pennsylvania gas oil fraction, boiling in the range of 575 to 700"v F. at atmospheric pressure, was used as the anti-tack component in the finished uid. This 575 to 700 F. material comprised approximately 2 per cent of the Bradford crude. It had '7.5 centistokes viscosity at 100 F., a flash point of 330 F., a pour point of +20 F., and an aniline point of 175 F.

A solvent dewaxing operation was carried out on each of these components separately. or in 14 thefratio ofY Bf'parts by weight of'lanti-tackcioil to'"7 ipartsilziy weight of .the .,base. oil :if used together. The procedure used was to charge the oil and: methylethylketone in the'.ratio/oi. 1 part by volumeofmilto 2 .partsby volume :of ketone, to .a 'large' tank capable fof:being.--1.efrig erated, the.methylethylketone.y serving vas-an1dil uent and *'antisolvent; 'for rwax, enabling the wax to separate from the oil at low temperatures much more readily than if the wax were .caused to separate from the. oil alone. .In order to facilitate c`ry`stallization o'f the .wax and subsequent filtration, 'one pound' of alter aid was added per 50 pounds of oilcharged. The cooling tank was equipped .witha suitable ragitating 'device such as a sti'rrer.4 The "first Step .inthe cooling process `consisted i'nci'rculating'fbrine or other refrigerant ..through"coils` in 'thecoolin'g tank until the temperature'of'th'e 'oil and 'ketone mixture was loweredto from' about ill'to't" F. vor '30'F. 'At "this point, small 'pieces of solid carbon dioxide. were v:added directly tozfthe oil `Vslurry juntil' r'thetemperature had. been ioweredr-Fto .-751 F.

I A` leaf-type suctionV .lter iiittedY with. a. `.suitable canvas was thenfflowered.aintotthe oil/esclv'cntwax Ii'slurry :and suction, `efrom a .suitable vacuumpwnn'was applied: l:to the insideiof-.the lter leaf. The oilgand. lk'etonearrnixture :passed through "ithe .canvas lter cloth, .and .thence flowed into a suitable receiver .-.to :which .the suction fwas applied. ithe.` asepar-ated .'Wax :rremained V"either-.on .the outside of the .filters-:as a cake; nor :as a` semisolid v mass inthe tank.

` The waxfree oil-.ketone mixture was thenrpa-ssed lthrough a flash :strippen .causing -distillatiomof -th'e ketone..andleaizinggthenstripped oil substantially ketone-free. 'Illiegoiluwas then `acid-.trcated vexactly as outlined zin. Example .Iuabova ,The .resulting wax-free ,aromatic-free loils had the .following properties, depending on whether .the base oil and anti-tackrwere treated separately .Gr.rst blended, together to .make the vbase stock.:

"Property TPasef'Oil "Anti-taek Viscosity at 100 F `es 1.9 7. 5 2. 7 Aniline Point F 180 193 184 A. S. T. M. Slope-. 0.81 0.82 0.81 Pour Pointku.. F -75 -75 -75 Flash Point F-. 200 330 210 1 No cloud visible above the temperatures listed.

yet been blended, they were then mixed in the r 3:7 ratio of anti-tack to base oil, by weight. To the resulting base stock was added 5.2 weight per cent Polybutene B-12, 0.2 weight Vper cent Paranox 441 oxidation and corrosion inhibitor, and 1.0 per cent tricresyl phosphate. Polybutene B-12 is a polymerized isobutylene of approximately 10,000 to 12,000 molecular weight. The tricresyl phosphate was employed l5 to improve the load-bearing capacities and wear'-y resistance characteristics of the finished hydraulic fluid.

The mixture of these various components was stirred and heated at 100 to 150 F. for about one hour, after which time the fluid was iiltered through several thicknesses of lter paper. The

' resulting finished hydraulic fluid had the following properties:

Viscosity at 130 F. 10.0 centistokes Viscosity at 100 F. 14.5 centistokes Viscosity at 40 F. 500 centistokes A. S. T. M. slope 130 to Aniline point 184 F.

Pour point -75 F.

Cloud point -75 F.

Flash point 210 F.

Fire point 225 F.

Neutralization number 0.08 mg. KOH per gm. oil

The improved hydraulic fluids of the present invention may also be given antirusting properties by incorporating specific organic materials which form adherent and impervious films on metals. Degras is a common constituent of such materials. Certain metal naphthenates are also sometimes used. In other cases, thepresence of organic materials forming water-in-oilremulsions afford some relief from rusting in the presence of moisture.

It is recognized that polymers have previously been added to mineral oils. Heretofore, however, the purpose has been to lower the viscositytemperature coefficient with the least possible increase in viscosity of the base stock. Moreover, in those cases where there have been large in creases in viscosity brought about by the addi,-

ti-on of polymeric substances, the product may or m-ay not have been improved with regard to viscosity-temperature c'oeiiicient, or A, S. 'I'. M. slope. Usually such uids are characterized more as semisolids, or plastic iluids, or as gels, rather th-an .as a limpid stable fluid capable of absorbing, dissipating, or transmitting large amounts of hydraulic energy without undergoing excessive changes in viscosity in use. Such previou'sfvi-scous or"^thickened materials have not been generally useable over a wide temperature range, such as, fork example, from 40 F. or lower-to +200 F.- or higher, inasmuch as they become gelsor sol-ids at the low temperature, and show considerable loss in viscosity with use at high temperatures; that is, they are characterized by poor visc-osity-shear stability.

The present invention obviates the foregoing disadvantages by proper control of (1) the nature of the base stock, (2) the solubility and molecular weight of the'polymer, and (3) the amount of polymer employed.

I claim:

A composition of mattei` usable as a hydraulic iiuid comprising a major portion of high boiling isoparainic hydrocarbons boiling between about 400 and 700y F. blended with a relatively small amount s-uillcient to change the viscosity index thereof substantially, of a polymer of a low boiling olen .said polymer having a molecular Weight above about 5000 and a polymerzed acrylic acid ester of a saturated alcohol.

MERRELL `ROBERT FENSKE.

REFERENCES CITED The following references are of record in the iileof this patent:

rUNITED STATES PATENTS 

